Air Pollution Lowers Baby's Birth Weight

Maternal exposure to air pollution during pregnancy was linked with low birth weight in their offspring, a worldwide study determined.

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This is a meta-analysis designed to quantify the association between maternal exposure to particulate air pollution and term birth weight and low birth weight.

Maternal exposure to particulate pollution was associated with low birth weight at term across study populations.

Maternal exposure to air pollution during pregnancy was linked with low birth weight in their offspring, a worldwide study determined.

In an analysis that included more than 3 million births, an increase of 10-µg/m3 in airborne particulate matter was associated with a slight but significant increase in low birth weight (OR 1.03, 95% CI 1.01 to 1.05, P<0.001), according to Payam Dadvand, MD, PhD, of the Center for Research in Environmental Epidemiology in Barcelona, and colleagues.

That degree of increase in pollution also had a negative association when birth weight at term was considered a continuous outcome variable ( −8.9 g, 95% CI −13.2 to −4.6), the researchers reported online in Environmental Health Perspectives.

"The estimated combined associations, although relatively small, could be of major public health importance considering the ubiquitous nature of particulate air pollution exposure and therefore the potential for considerable population attributable risks, particularly given evidence of both perinatal and life-long effects of low birth weight on health," they stated.

It has become increasingly evident that air pollution is associated with a number of potential pregnancy complications ranging from stillbirth to congenital defects.

However, previous studies assessing the effects on birth weight have been inconsistent in design, confounders, and reported outcomes, which has limited the ability of policymakers in their efforts at regulation.

To provide a clearer estimate of these risks, Dadvand and colleagues analyzed data from 14 centers in the International Collaboration on Air Pollution and Pregnancy Outcomes, combining effect estimates from the included centers and taking into account the possibility of between-center heterogeneity.

Participating centers were in North and South America, Europe, Asia, and Oceania.

In the 13 centers that reported associations between particulate matter with aerodynamic diameter less than 10 µm (PM10), consistent associations were seen with low birth weight after adjustment for socioeconomic status and maternal age, ethnicity, and smoking (OR 1.02, 95% CI 1.01 to 1.04, P=0.01).

Nine of the centers also reported estimates of the association between low birth weight and PM10 exposure according to the trimester of exposure.

Meta-analyses of these estimates found odds ratios of 1.01 (95% CI 1.01 to 1.01) for the first trimester, 1.01 (95% CI 1.01 to 1.02) for the second trimester, and 1.02 (95% CI 1.01 to 1.02) for the third, all of which were significant (P<0.001).

Considerable heterogeneity between the various centers' estimates existed in all these analyses, the researchers noted.

There also was residual heterogeneity when they calculated meta-regression coefficients accounting for other factors such as the PM2.5/PM10 ratio, median PM2.5 levels, and whether the centers used temporal or spatiotemporal analyses.

This heterogeneity may reflect geographical variations in levels of pollution, they suggested.

The study was limited by its univariate analysis. The effect estimates were insufficient for multivariate analysis, so confounding could have been present.

In addition, data on environmental and personal exposures at the individual level were unavailable.

Nonetheless, these findings "support an adverse impact of maternal exposure to particulate pollution on fetal growth" and can "increase the confidence of policy-makers when summarizing existing evidence and translating it into policy," Dadvand and colleagues concluded.

The study received support from the U.S. Environmental Protection Agency, the National Institute for Environmental Health Sciences, the Wellcome Trust, and the Spanish Ministry of Science and Innovation.

The authors reported no conflicts of interest.

Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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